[iceberg] Fix UnsupportedOperationException reading tinyint and smallint columns

[ArnavBalyan]

Purpose

• Iceberg toByteBuffer encodes tiny and small int as 4 byte little endian int, but IcebergConversions.toPaimonObject has no matching case and throws UnsupportedOperationException.
• Occurs when the type is used as a partition column and decoded back into Paimon objects.
• Add support for the same.

Tests

• Unit tests

[ArnavBalyan]

cc @JingsongLi thanks! :)

[JingsongLi]

+1